Field of the Invention
The present invention relates to a cooling apparatus and cooling control method for exhaust gas recirculation (EGR) gas and engine oil, in which an EGR cooler for cooling EGR gas and an oil cooler for cooling engine oil are integrated into one module, by which EGR gas can be cooled and engine oil can be heated and cooled.
Description of Related Art
An exhaust gas recirculation (EGR) cooler is an apparatus which reduces the amount of NOx by lowering the temperature of hot EGR gas and an oil cooler is an apparatus which cools oil so that the temperature of oil can stay at a suitable level. The EGR cooler and the oil cooler are very important heat exchangers of an engine.
Coolant (antifreezing solution) performs a very important role in the control over the temperature of fluids or gas through heating and cooling. In particular, the coolant in the oil cooler serves to maintain the temperature of oil at a certain level adequate to operation of the engine. The engine oil is a very important lubricating element for kinematic friction systems in the engine which require lubrication, including an oil pump, a cylinder block, a piston, a crankshaft and most parts of the engine. When the temperature of the oil is low, the friction among these components is worsened due to the low kinematic viscosity of the oil. Accordingly, in a cooling state while the vehicle is being driven, a rapid rise in the temperature of the oil can reduce frictional force, thereby contributing to an improvement in the fuel efficiency of the vehicle.
In addition, the EGR cooler is a very important apparatus for reducing the amount of exhaust (NOx). The coolant has the first role of lowering the temperature of the EGR gas by absorbing the high-temperature heat of the EGR gas. When the coolant is introduced into the oil cooler during cooling, it can perform the second role of raising the temperature of the oil by transferring the heat to the oil.
However, the source of heat required for raising the temperature of the engine oil is the energy of combustion gas (including EGR gas). Heat transferred from the combustion gas can be regarded as the most important factor to raise the temperature of the coolant and the oil. Therefore, there may be a variety of methods that can more rapidly raise the temperature of fluid using the heat of the engine. It is possible to help raise combustion efficiency and fuel efficiency to be optimal levels by controlling the temperatures of the EGR gas, the coolant and the oil.
Referring to FIG. 1, in the related art, an EGR cooler 1 and an oil cooler 2 form separate cooling systems. EGR gas is cooled through the EGR cooler 1 or bypasses the EGR cooler 1 before being discharged depending on the control condition. Coolant constantly flows to the EGR cooler 1, and after having passed through the cooler, forms a cooling circuit that leads to the oil cooler 2.
Oil is taken into and discharged from an oil pump 4 before entering the oil cooler 2 where the oil is cooled. Afterwards, the cooled oil passes through an oil filter 5 and forms a lubricating circuit which leads to an apparatus which requires lubrication.
Although the EGR cooler 1 and the oil cooler 2 indirectly exchange heat via the coolant, it takes a long time to raise the oil temperature during cooling, and the discharge pressure of the oil pump 4 is increased. Consequently, the pressure of the oil, the surface pressure of friction systems, and the friction force of a driving system are increased, which are problematic. The oil having a low temperature forms high kinematic viscosity and high oil pressure, which decreases the friction resistance of engine components and causes noise, thereby decreasing the endurance of the engine.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.